Flame-retardant material comprising a biopolymer

ABSTRACT

Flame-retardant material comprising:
         a matrix comprising, preferably consisting of, at least one organic polymer;   a flame-retardant agent selected from metal hydroxides; and   a coupling agent forming an interface between the matrix and the flame-retardant agent;
 
wherein the matrix comprises at least 50% by mass of at least one biopolymer, and the coupling agent consists of a copolymer of ethylene and vinyl acetate (EVA), comprising at least 40% by mass of vinyl acetate (VA), grafted with maleic anhydride.
       

     Electrical installation box or electrical cable tube, conduit, comprising said material. 
     Use of said material for manufacturing electrical installation boxes or electrical cable tubes.

FIELD OF THE INVENTION

The invention relates to a flame-retardant material comprising abiopolymer, more precisely a thermoplastic biopolymer, also referred toas a bioplastic.

More specifically, the invention relates to a flame-retardant materialsuitable for being moulded or extruded. This material comprises anorganic matrix comprising at least 50% by mass of at least onebiopolymer, a flame-retardant agent selected from metallic hydroxides(metal hydroxides), and a coupling agent forming as an interface betweenthe matrix and the flame-retardant agent.

The material according to the invention particularly can be applied inelectrical devices such as installation boxes and cable managementsystems.

PRIOR ART

Plastics, or more precisely thermoplastic polymers, are used in numerousindustrial sectors and particularly in the electrical industry; theproperties of these plastics have a considerable impact on the ProductEnvironmental Profile, particularly on the CO₂ impact and theconsequences thereof on global warming.

Moreover, these plastics, such as poly(ethylene) (PE), polyvinylchloride (PVC), and polypropylene (PP) are mostly obtained frompetroleum, and pose numerous problems particularly associated with thedepletion of oil reserves, and the processing of wastes containing thesesubstances.

The use of biopolymers or bioplastics, which does not involve any of theproblems mentioned above has thus increased considerably. Note that theterm biopolymer refers to a polymer obtained exclusively from livingorganisms, generally plants, or a polymer synthesised from renewableresources, generally plant-based. Biopolymers or bioplastics, aregenerally biodegradable and suitable for composting, and the wastethereof is readily disposable.

An example of such a bioplastic is poly(lactic acid) which is a plasticobtained by polymerising lactates particularly obtained by fermentingstarch.

Although, at the present time, the price of bioplastics is higher thanthat of petroleum-based plastics, the price thereof can be expected tobecome competitive in the future.

For numerous uses of plastics, regardless of whether they arebiodegradable or not, it is necessary to incorporate a flame-retardantagent therein.

In this way, the flame-retardant properties applicable to plastics usedin electrical devices are defined by IEC (“InternationalElectrotechnical Commission”) standards such as the IEC 60695-2-1standard.

The most commonly used flame-retardant agents are halogenatedflame-retardant agents; however, these halogenated flame-retardantagents involve the major drawback of generating corrosive and toxiccompounds such as dioxins during the combustion thereof, for exampleduring the incineration of waste containing these substances and thusshould be avoided.

Flame-retardant agents not containing halogens are, in particular,aluminium polyphosphate, and metal hydroxides such as aluminiumtrihydroxide (ATH). Compared to halogenated flame-retardant agents,metal hydroxides such as ATH have low fume, smoke, emissions and are nottoxic. However, polymer compositions containing these compounds, even invery small quantities, have very insufficient mechanical properties,i.e. a very low mechanical resistance, strength, and a modulus inflexure less than 1000 MPa, making them unsuitable for many uses.

The document U.S. Pat. No. 4,525,494 mentions the use of aluminiumtrihydroxide (ATH) coated with fatty acid in polymer compositions with ahigh modulus in flexure. However, the cost of this coatedflame-retardant agent is high. Moreover, coated flame-retardant agentscause a significant stress whitening effect in polymer compositionscontaining same.

To remedy this drawback, the document WO 01/51554 describes aflame-retardant polymer composition consisting of a polyethylene, one ora plurality of binder(s) including a flame-retardant agent such asaluminium trihydrate. At least 5% by weight of the polymers are modifiedwith maleic anhydride. This polymer composition is used in theelectrical industry.

The documents EP 1 544 250, EP 674 627, EP 1 795 561, US 2008/0108729,EP 1 816 169, EP 1 361 039, and WO 2008/058020 describe compositionswherein the non-plastic filler content is greater than 30%; the rigiditythereof is high but the flexibility thereof is very low with anelongation at break of less than 3%.

Such a flexibility is markedly insufficient to enable the use of thesecompositions in moulding or extrusion methods especially for preparingitems suitable for use in the electrical industry.

There is thus a need for a flame-retardant material, i.e. complying withthe IEC standard, IEC 60695-2-1 in force on 30 Mar. 2011 comprising apolymer matrix consisting partly or completely of a biopolymer, and aflame-retardant agent chosen from metal hydroxides such as aluminiumtrihydroxide (ATH), which has an enhanced flexibility with a greaterelongation at break.

There is also a need for such a material having, in addition to agreater elongation at break, satisfactory mechanical propertiesrepresented for example by a high E-modulus and a high maximum strength(complying with ISO 527-1 and following).

There is also a need for such a material which can be readily moulded orextruded to prepare, in a simple, reliable and non-polluting manner, ata low cost, items, even of complex shapes, and particularly items usedin the electrical industry such as installation boxes, cable managementsystems etc., these items being rigid and shock-resistant.

The goal of the invention is that of providing a flame-retardantmaterial fulfilling, among other things, the needs listed above. The aimof the invention is also that of providing a flame-retardant materialwhich does not have the drawbacks, failings, limitations anddisadvantages of the compositions according to the prior art.

SUMMARY OF THE INVENTION

This goal and others are met, according to the invention, by aflame-retardant material comprising:

-   -   a matrix comprising, preferably consisting of, at least one        organic polymer;    -   a flame-retardant agent selected from metal hydroxides; and a        coupling agent acting as an interface between the matrix and the        flame-retardant agent;        wherein the matrix comprises at least 50% by mass of at least        one biopolymer, and the coupling agent consists of a copolymer        of ethylene and vinyl acetate (EVA), comprising at least 40% by        mass of vinyl acetate (VA), grafted with maleic anhydride.

This copolymer no longer having the typical properties of an EVA, andhaving a high vinyl acetate content may also be named EVM according toelastomer terminology.

The term flame-retardant material in the sense of the inventiongenerally indicates that this material complies with the IEC-60695-2-1standard in force on 30 Mar. 2011 (with a glow wire at 850° C. on asheet, plate thickness greater than 1.5 mm).

Advantageously, the material has an elongation at break measured usingthe procedure specified in the ISO 527 standard in force on 30 Mar. 2011greater than 4.5%.

Advantageously the ethylene and vinyl acetate copolymer comprises 55% to75% by mass, for example 60% by mass, of vinyl acetate. An example ofsuch a copolymer is the copolymer available from LANXESS™ as Levamelt™600.

Advantageously, the ethylene and vinyl acetate copolymer is grafted withmaleic anhydride in a manner known in the art, at a ratio of 0.1% to 10%by mass for example.

Advantageously, the flame-retardant agent is selected from aluminiumtrihydroxide (ATH), magnesium hydroxide, calcium/aluminium hydrate, tinoxide hydrate or phlogopite, and mixtures thereof (see EP 1 544 250, WO01/51554).

Generally, the flame-retardant agent is in the form of particles havinga mean diameter (d₅₀) in the range from 0.1 to 10 μm, preferably in therange from 0.5 to 8 μm, more preferably in the range from 1 to 5 μm.

Advantageously, the biopolymer is selected from poly(lactic acid) PLAand polyester biopolymers other than poly(lactic acid).

The term poly(lactic acid) refers to all types of polylactic acid. Theterm polylactic acid covers poly(L-lactic acid) or PLLA consisting ofL-lactic acid structural units, poly(D-lactic acid) or PDLA consistingof D-lactic acid structural units, or poly(DL-lactic acid) consisting ofD-lactic acid and L-lactic acid structural units, and mixtures of two ormore thereof.

The proportion of D isomers and L isomers of the poly(lactic acid) usedaccording to the invention is generally such that the ratio between thetwo isomers is preferably from 100:0 to 90:10; more preferably, thisratio is from 0.5:99.5 to 6:94.

The term poly(lactic acid) also refers to copolymers of lactic acid withanother monomer selected for example from α-hydroxycarboxylic acids,aliphatic diols, and aliphatic dicarboxylic acids.

The biodegradable polyesters also referred to as bioplastic polyestersother than poly(lactic acid) may be selected from biodegradablealiphatic polyesters and biodegradable aliphatic aromatic polyestersother than poly(lactic acid). Examples of biodegradable aliphaticpolyesters other than poly(lactic acid) include aliphatic polyestersobtained by condensing an aliphatic diol and an aliphatic dicarboxylicacid, polyesters obtained by ring-opening polymerization of cycliclactones, synthetic aliphatic polyesters, and the like. A particularexample of such a biodegradable polyester or bioplastic polyester ispoly(butylene succinate) (PBS).

Examples of biodegradable aliphatic aromatic polyesters includealiphatic aromatic polyesters comprising an aromatic dicarboxylic acidconstituent, an aliphatic dicarboxylic acid constituent, and analiphatic diol constituent.

Advantageously, the biopolymer of the matrix consists of poly(lacticacid).

Advantageously, the matrix comprises at least 60% by mass of at leastone biopolymer, preferably the matrix comprises at least 90% by mass ofat least one biopolymer, or even consists of one or a plurality ofbiopolymer(s) such as poly(lactic acid).

Alternatively, the matrix may further comprise one or a plurality ofother polymer(s) which are not biopolymers in order to reduce thebiodegradability of the material and/or to enhance some of theproperties of the material. Examples of such polymers arepolycarbonates, Acrylonitrile-Butadiene-Styrene copolymers (ABS),polystyrenes, and polypropylenes.

Advantageously, the matrix represents from 35% to 75% by mass,preferably from 50% to 65% by mass of the total material mass.

Advantageously, the flame-retardant agent represents from 25% to 65% bymass, preferably from 35% to 50% by mass of the total material mass.

Advantageously, the coupling agent represents from 1% to 25% by mass,preferably from 4% to 10% by mass of the total material mass.

Besides the flame-retardant agent, the material according to theinvention may comprise one or a plurality of additive(s) and/orfiller(s). In this way, the material according to the invention mayfurther comprise at least one anti-ultraviolet stabilising agent(UV-stabilizer) such as Chimassorb™ from Ciba Specialty Chemicals.

The material according to the invention may further comprise at leastone colouring substance selected from dyes and pigments to give thematerial the desired colour.

The material according to the invention may further comprise at leastone anti-hydrolysis additive to prevent the hydrolysis of the materialand enhance the long-term stability thereof. Such an anti-hydrolysisagent may be selected from polycarbodiimides such as Stabaxol™ orRHENOGRAN™ from Rhein-Chemie™.

Obviously, the fillers and additives mentioned above are merely given asexamples. Further fillers and additives may be included in the materialaccording to the invention and may be readily selected by the manskilled in the art in view of the properties sought in the material.

Advantageously, the material according to the invention may consist (becomposed), in percentages by mass, of 45% to 65% of at least onebiopolyester such as poly(lactic acid), 30% to 45% of at least one metalhydroxide such as aluminium trihydroxide, 6% to 8% of coupling agent,and optionally one or a plurality of additive(s) and/or filler(s), thetotal percentage by mass of the biopolyester, the metal hydroxide, thecoupling agent and of the additive(s) and/of filler(s) being 100% bymass.

Advantageously, the material according to the invention may be preparedby mixing the organic polymer, the flame-retardant agent, the couplingagent, and optionally one or a plurality of additive(s) and/or filler(s)homogeneously, preferably by means of an extrusion mixing method.

The flame-retardant material according to the invention has not beenpreviously described in the prior art; it particularly differs from theflame-retardant materials according to the prior art in that itcomprises a specific coupling agent, consisting of an ethylene and vinylacetate copolymer comprising at least 40% by mass of vinyl acetate,grafted with maleic anhydride. As mentioned above, a preferred EVAcopolymer comprises from 55% to 75% vinyl acetate, for example 60% vinylacetate. This proportion of VA is markedly superior to that of standardEVAs only containing approximately 30% EVA.

The material according to the invention does not have the drawbacks,failings, limitations and disadvantages of the flame-retardant materialsaccording to the prior art, particularly flame-retardant materialsaccording to the prior art based on biopolymers containing metalhydroxides as flame-retardant agents.

The material according to the invention solves the basic problem of theflame-retardant materials according to the prior art, which is that ofthe insufficient flexibility thereof. More specifically, the elongationat break of the flame-retardant material according to the invention issignificantly enhanced with respect to the elongation at break offlame-retardant materials according to the prior art. It wassurprisingly observed that the material according to the inventiongenerally had an elongation at break greater than 4.5%, which is verymarkedly greater than the elongation at break values of materialsaccording to the prior art.

In addition to this excellent and unexpected flexibility, the materialaccording to the invention has, overall, excellent mechanicalproperties, for example a Young's modulus, E-modulus greater than 1900MPa and a maximum strength (stress at break) greater than 20 MPa.

The excellent and surprising flexibility of the material according tothe invention is demonstrated in the examples given hereinafter whereinover fifty formulations were tested, including numerous formulationsdescribed in patent applications and in the literature and fourformulations according to the invention. Surprisingly, it was foundthat, of all the formulations tested, only the formulations according tothe invention were suitable for obtaining an excellent flexibility withan elongation at break greater than 4.5%.

Without intending to be linked with any theory, it can be consideredthat, according to the invention, it was possible to obtain asurprisingly flexible flame-retardant material through the use in thismaterial of a specific coupling agent which, due to the particularcomposition and structure thereof, imparts an excellent flexibility tothe organic matrix and, at the same time, provides coupling between thematrix and the mineral flame-retardant agent which, according to theinvention, is not treated.

Indeed, in the coupling agent according to the invention, it was foundthat the EVA copolymer imparted excellent flexibility to the organicmatrix and particularly to the constituent biopolymers thereof, such asPLA, whereas grafting with maleic anhydride provided satisfactorycoupling with the metal hydroxide.

Similar results may be obtained with other polar copolymers, such asethylene butyl, methyl or ethyl acrylate (EBA, EMA, EEA), grafted withmaleic anhydride.

Furthermore, the high content of vinyl acetate, which is the polarcomponent of EVA ensures excellent mixing with the organic matrix andparticularly with the constituent biopolymers thereof, such as EVA.

In the material according to the invention, when mixing the variousconstituents for example by extrusion, the coupling agent binds with(attaches to) the surface of the flame-retardant agent via maleicanhydride functions of the coupling agent.

The coupling agent thus forms a flexible interface between theflame-retardant agent and the organic polymer matrix, more specificallybetween each of the flame-retardant agent particles and the organicpolymer matrix. Furthermore, the coupling agent imparts flexibilityproperties to the matrix. For example, the material according to theinvention has a markedly higher elongation at break than that of purePLA (approximately 3%) whereas it may contain significant quantities ofmetal hydroxide flame-retardant agent of up to 40%, or even 50% by mass,for example.

The raw materials of the material according to the invention are readilyavailable and the cost thereof is moderate. The material according tothe invention is non-toxic particularly in that the flame-retardantagent contained therein is selected from metal hydroxides such as ATHwhich do not contain halogens and do not generate toxic gases.

The raw material of the matrix is entirely or mainly of biologicalorigin (biopolymer) and has a low impact on greenhouse gas emission.Since bioplastics from the material according to the invention arebiodegradable and metal hydroxides are non-toxic, the material accordingto the invention can be classified as a recyclable material.

The material according to the invention is suitable for manufacturing,flame-retardant products, items at a reasonable price and in anon-polluting and environmentally-friendly manner particularly with lowgreenhouse gas emission.

Due to the excellent mechanical properties thereof and particularly theexcellent flexibility thereof, it is possible with the materialaccording to the invention to manufacture injection-moulded and/orextruded items, such as electrical equipments, installation boxes orelectrical installation devices such as lines, conduits, and cablemanagement systems, trunkings, cable tubes and cable conduits which haveflame-retardant properties and which are flexible and shock-resistant.

The material according to the invention may be prepared by mixing theraw materials intended to form the material, i.e. the organic polymer,the flame-retardant agent and the coupling agent generally at a hightemperature above the softening point of the polymers, until ahomogeneous mixture of these raw materials is obtained.

Advantageously, all the constituents were dried before processing, forexample in a vacuum oven at 60° C. for 6 hours.

In general, the process starts by mixing or kneading the polymer(s) andthen adding the other raw materials thereto. This mixing may be carriedout in any type of mixer, for example an extruder or a batch blender.This mixing may be carried out preferably by means of an extrusionmixing method in an extruder as shown in FIG. 1.

This extruder comprising a first hopper (1) through which the feed ofthe polymer(s) of the material according to the invention is carriedout. This hopper (1) opens into a first feed zone (2) of the sheath (3)of the extruder wherein the endless extrusion screw (4) is rotated.

The sheath (3) of the extruder is generally heated to a temperatureabove the softening point of the polymer(s), for example to atemperature from 150° C. to 190° C.

The polymer(s) is/are conveyed by the extrusion screw and successivelyundergo(es) compression in a first compression area (5), then a firstkneading in a first kneading area (6) before reaching a second feed area(7) which is supplied by a second hopper (8) with the filler(s) intendedto be incorporated in the material according to the invention.

The material thus comprising the polymer(s) supplemented with thefiller(s) is conveyed by the extrusion screw (4) into a secondcompression area (9) then into a second kneading area (10) then into athird compression area (11) before being discharged from the extrudervia a die (12).

A vacuum is produced in the extruder sheath by means of a connectionpiece, tapping, (13).

The metal hydroxide is generally introduced into the hopper (8), and thecoupling agent into the hopper (1). The additives may be introducedeither into the hopper (1), or into the hopper (8) according to the typeof additive.

At the outlet of this extruder, the material according to the inventionis generally in the form of granules or pellets. It may then be used forpreparing various items of all possible sizes and shapes. These itemsinherently have all the advantageous properties of the material fromwhich they were prepared.

These items may be prepared by any plastics technology method, forexample by moulding or by extrusion, particularly by injection mouldingor by profiles extrusion. In particular, these items may be used in theelectrical industry, in applications wherein flame-retardant propertiesare important. These items, parts, objects may be items, parts, objectsaccording to the invention, for applications in cable management systemssuch as installation boxes and electrical cabinets, trunkings, cableconduits or electrical apparatus boxes or housings such as sockets,circuit breakers, switches or electronic devices such as sensors andregulators.

In this way, the invention also relates to an electrical installation(e.g. switchgear) box or an electrical cable, tube, conduit, comprisinga material according to the invention as described above.

Due to the material according to the invention, these items have aconsiderably better environmental profile than items prepared frommaterials according to the prior art and are recyclable or suitable forcomposting.

The invention thus further relates to the use of the material accordingto the invention for manufacturing electrical installation boxes orelectrical cable tubes, conduits.

The invention will be understood more clearly on reading the followingdescription of the embodiments of the invention in the form of examplesdescribing materials according to the invention, and comparativeexamples describing materials not according to the invention andproviding test results particularly for elongation at break testsconducted on these materials according or not according to theinvention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1, described above, is a sectional side view of an extruder mixerused for preparing the materials according to the invention.

FIG. 2 is a graph showing the elongation at break (as a %) of fourmaterials not according to the invention prepared from formulationsnamed A015, A018, A020, and A028 (see Table 7) comprising 6% EVA andBiomax™ Strong 120 available from DuPont™ which is aflexibility-modifying agent.

FIG. 3 is a graph showing the elongation at break (as a %) of fourmaterials according to the invention prepared from formulations namedA048, A049, A050, A051 (see Table 6).

For each of the four materials A048, A049, A050, and A051, the threebars (I+2 days; I+12 days; and I+1 month) give elongation at breakvalues for elongation tests conducted two days, 12 days and one monthafter preparing the material, respectively.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS Examples

Hereinafter, materials are prepared from compositions or formulations,identified by the reference AXX.

These materials are prepared by extrusion mixing as described above, andare in granule form. To obtain the standardised properties, the driedgranules were converted into test specimens, draw bars of the typedefined in the ISO 527-1A standard (in force on 30 Mar. 2011).

Firstly, materials are simply prepared from formulations consisting ofPLA and ATH as the flame-retardant agent in a variable proportionranging from 10% to 40% by mass.

Mechanical tests (ISO 527) and a fire-resistance test (IEC-60695-2-1 inforce on 30 Mar. 2011) at 850° C. with a sheet thickness of 1 mm and 2mm were carried out on these materials: the material comprising 30% bymass of ATH has self-extinguishing properties; however, the materialsobtained are very brittle with an elongation at break below 1%.

A copolymer (EVA 1: EVA with a VA content of 27.5%) available asEscorene™ 02528 CC from Exxon Mobil) and a grafted copolymer (EVA-MAH1:EVA with a VA content of 28%, grafted with maleic anhydride, availableas Fusabond™ C 190 from DuPont™) are added to the formulation to enhancethe flexibility of the material. This technology is known in thetechnical field in order to obtain a satisfactory interface between theplastic matrix and the metal hydroxide filler.

The two copolymer materials were each tested independently, and incombination with percentages ranging from 3% to 20% by mass in theformulation.

The materials tested in this way are materials prepared from theformulations named A016, A014, A013, and A018.

The formulations and the results of the mechanical tests and thefire-resistance test carried out on materials prepared from theseformulations are given in Table 1 below.

TABLE 1 A016 A014 A013 A018 PLA 57% 60% 65% 54% ATH 1 40% 30% 30% 40%EVA 1  3%  5%  0%  6% EVA-MAH 1  0%  5%  5%  0% Elongation 0.76%  1.55%   1.13%   0.93%   at break (“Er”) E-Modulus 7722 MPa 2584 MPa 3826MPa 6570 MPa Maximum  56 MPa  25 MPa  35 MPa  51 MPa strength Fire testPass Fail Fail Pass PLA: Natureplast ™ PLI003 from Natureplast ™ ATH 1:Alolt ™ 59AF, from Magyar Alumina ™ EVA 1: Escorene ™ 02528CC from ExxonMobil ™, EVA with a VA content of 27.5%. EVA-MAH 1: Fusabond ™ C190 fromDuPont ™, EVA with a VA content of 28%, grafted with maleic anhydrideMAH.

The best results in terms of flexibility are obtained with the materialprepared from the formulation (A014) consisting of 5% EVA, 5% EVAgrafted with maleic anhydride, 30% ATH and 60% PLA with an elongation atbreak value of 1.55%, which is still not sufficient, however.

The conclusion is that EVA 1 and EVA-MAH 1 do not impart enoughflexibility to the formulation (formulations A013, A014, A016, A018).

To obtain a more flexible polymer, known flexibility additives weretested such as Biomax Strong™ 120 available from DuPont™, and a PBS(PBS 1) available from Natureplast™ SA as Natureplast™ PBI 003, but manyothers are known in the industry.

The materials tested in this way are materials prepared from theformulations named A022, A019, A020, and A035.

The formulations and the results of the mechanical tests and thefire-resistance test carried out on materials prepared from theseformulations are given in Table 2 below.

TABLE 2 A022 A019 A020 A035 PLA 95%  57% 54% 45% ATH 1 0% 40% 40% 40%Biomax ™ 5%  3%  6%  0% Strong 120 PBS 1 0%  0%  0% 15% Elongation 127% 0.81%   0.76%   0.85%   at break (“Er”) E-Modulus 3033 MPa 8704 MPa 7120MPa 6391 MPa Maximum  56 MPa  56 MPa  49 MPa  45 MPa strength PBS 1:Natureplast ™ PBI 003 biodegradable polyester from Natureplast ™ SA.

It was demonstrated that adding Biomax Strong™ 120 to PLA increases theelongation at break of the material prepared from this formulation from3% to 127% (A022). However, adding metal hydroxide to PLA comprisingknown flexibility additives, for example PLA supplemented with Biomax™Strong 120, destroys all the flexibility properties of the material andthe elongation at break drops hugely to less than 1% (A019-A020 andA035).

Combining known flexibility additives (Biomax Strong™ 120, PBS) withcoupling agents grafted with maleic anhydride (EVA-MAH 1: Fusabond™C190) in PLA also does not solve the problem (Formulations A021, A028:see Table 3 below).

Biomax Strong™ was also tested combined with Stabaxol™ P, ananti-hydrolysis agent described in the patent EP-B1-1 544 250. Althoughthe reduction in the molecular mass is somewhat lower, the material isstill brittle (Formulation A024: see Table 3 below).

TABLE 3 A021 A028 A024 PLA 54%  48%  52%  ATH 1 40%  40%  40%  Biomax ™3% 6% 3% Strong 120 EVA-MAH 1 3% 6% 0% Stabaxol ™ P 0% 0% 5% Elongation1.14%   1.32%   1.22%   at break (“Er”) E-Modulus 3109 MPa 1438 MPa 2670MPa Maximum  27 MPa  17 MPa  23 MPa strength Fire test Fail Fail FailStabaxol ™ P, RHENOGRAN ™ PCD-50/EVA, from Rhein-Chemie ™,polycarbo-diimide anti-hydrolysis agent.

Various types of ATH, including products of submicronic size (Apyral™200SM from Nabaltec™) which are precipitated (Apyral™ 60CD, Apyral™200SM from Nabaltec™) from a solution rather than being ground, weretested without any positive impact on the elongation at break(Formulations A030-A033: see Table 4 below)

TABLE 4 A028 A031 A033 A036 PLA 48%  48%  48%  54%  ATH 1 40%  0% 0% 0%ATH 2 0% 40%  33%  0% ATH 3 0% 0% 7% 0% ATH 4 0% 0% 0% 40% BiomaxTM 6%6% 6% 6% Strong 120 EVA-MAH 1 6% 6% 6% 0% Elongation 1.32%   1.13%  0.57%   0.31%   at break (“Er”) E-Modulus 1439 MPa 1621 MPa 2836 MPa4556 MPa Maximum  17 MPa  15 MPa  12 MPa  16 MPa strength ATH 2:Apyral ™ 60CD from Nabaltec ™ ATH 3: Apyral ™ 200SM from Nabaltec ™ ATH4: Apyral ™ 60 VS1 from Nabaltec ™, ATH with vinylsilane coating.

Coated metal hydroxides (such as those described in the patent EP-B1-1544 250) and known flexibility additives (Biomax Strong™ 120, PBS) werethen tested with PLA to overcome the problem.

In this way, the formulation A036 mentioned in Table 4 contains APYRAL™60 VS 1 from NABALTEC™ which is an ATH treated with vinylsilane. Theelongation at break of the material prepared from this formulation isbelow 0.5%.

A further ATH (ATH 5) provided with another coating (fatty acid)available from HUBER™ in the United States, as Hymod™ SB-432 ST1 alsoproduced poor results (Formulation 041 in Table 5 below).

Although these metal hydroxides having undergone a surface treatmentproduce a satisfactory interface between the matrix and the coated metalhydroxide, they do not impart the sought flexibility to the matrix.

TABLE 5 A028 A041 PLA 48%  54%  ATH 1 40%  0% ATH 5 0% 40%  Biomax ™Strong 6% 6% 120 EVA-MAH 1 6% 0% Elongation at 1.32%   0.91%   break(“Er”) E-Modulus 1439 MPa 4751 MPa Maximum strength  17 MPa  24 MPa ATH5: Hymod ™ SB-432 ST1 from Huber ™, ATH with a fatty acid coating.

It is thus noted, in view of the test results given above, that all themethods described above and known in the prior art did not provide thecomposition with sufficient flexibility.

Levamelt™ 600 is an EVA with a VA content of 60%. This content isgreater than that of standard EVA which has a VA content of 30%; in therubber industry, this compound is called EVM due to the rubberyproperties thereof.

Adding, at a rate of 6% or 8% by mass, Levamelt™ 600 grafted with maleicanhydride in the formulations A048 to A051 (see Table 6 below) producesa material according to the invention with an astonishingly goodelongation at break.

TABLE 6 A048 A049 A050 A051 PLA 51.5% 49.0% 49.5% 47% ATH 1 42.5%   45%42.5% 45% EVA-MAH 2   6%   6%   8%  8% Elongation 4.69% 5.01% 6.97%6.74%   at break (“Er”) E-Modulus 2153 MPa 2401 MPa 2012 MPa 1996 MPaMaximum  26 MPa  24 MPa  24 MPa  22 MPa strength Fire test Pass PassPass Pass EVA-MAH 2: Levamelt ™ 600 from Lanxess ™, EVA with a VAcontent of 60%, grafted with maleic anhydride MAH.

For comparison purposes, mechanical resistance tests and fire resistancetests are carried out on 4 materials not according to the inventionprepared from formulations A015, A018, A020, and A028.

The formulations and the test results are given in Table 7 below.

TABLE 7 A015 A018 A020 A028 PLA 64%  54%  54%  48%  ATH 1 30%  40%  40% 40%  EVA 1 6% 6% 0% 0% EVA-MAH 1 0% 0% 0% 6% Biomax 0% 0% 6% 6% Strong ™120 Elongation 1.03%   0.93%   0.76%   1.32%   at break (“Er”) E-Modulus5505 MPa 6570 MPa 7120 MPa 1438 MPa Maximum  52 MPa  51 MPa  49 MPa  17MPa strength Fire test Pass Pass Fail Fail PLA: Natureplast ™ PLI003from Natureplast ™ ATH 1: Alolt ™ 59AF from Magyar Alumina ™ EVA 1:Escorene ™ 02528CC from Exxon Mobil ™, EVA with a VA content of 27.5%.EVA-MAH 1: Fusabond ™ C190 from DuPont ™, EVA with a VA content of 28%,grafted with maleic anhydride MAH. Biomax Strong ™ 120 from DuPont ™.

Although the flame-retardant filler (ATH) content is lower informulations A015, A018 and A020 than in formulations A048 to A051according to the invention, the elongation at break remains very low forthese formulations, producing a brittle “plastic” (see FIG. 2).

On the other hand, EVA-MAH 2 has a surprisingly strong effect on theelongation at break, since the material prepared from the formulationsA048 to A051 containing EVA-MAH 2 exhibits an increase of approximately500% in the elongation at break as seen in FIG. 3.

With formulations A048 to A051 containing EVA-MAH 2, the materials(according to the invention) are no longer brittle at all.

The invention claimed is:
 1. A flame-retardant material, comprising: amatrix comprising an organic polymer; a flame-retardant agent comprisinga metal hydroxide; and a coupling agent forming an interface between thematrix and the flame-retardant agent; wherein: the matrix comprises atleast 90% by mass of a biopolymer; and the coupling agent consists of acopolymer of ethylene and vinyl acetate (EVA), said copolymer comprisingat least 40% by mass of vinyl acetate (VA), grafted with maleicanhydride.
 2. The material of claim 1, which complies with theIEC-60695-2-1 standard.
 3. The material of claim 1, having an elongationat break of greater than 4.5%, as measured using the procedure specifiedin the ISO 527 standard.
 4. The material of claim 1, wherein thecoupling agent comprises 55% to 75% by mass of vinyl acetate.
 5. Thematerial of claim 1, wherein the metal hydroxide is selected from thegroup consisting of aluminium trihydroxide, magnesium hydroxide,calcium/aluminium hydrate, tin oxide hydrate, phlogopite, and mixturesthereof.
 6. The material of claim 1, wherein the biopolymer is selectedfrom the group consisting of poly(lactic acid) and a polyesterbiopolymer other than polylactic acid.
 7. The material of claim 1,wherein the matrix further comprises an additional polymer which is nota biopolymer.
 8. The material of claim 1, comprising from 35% to 75% bymass of the matrix, relative to a total mass of the material.
 9. Thematerial of claim 1, comprising from 25% to 65% by mass of theflame-retardant agent, relative to a total mass of the material.
 10. Thematerial of claim 1, comprising from 1% to 25% by mass of the couplingagent, relative to a total mass of the material.
 11. The material ofclaim 1, further comprising an additive, a filler, or both.
 12. Thematerial of claim 1, consisting of in percentages by mass: 45% to 65% ofat least one biopolyester; 30% to 45% of at least one metal hydroxide;6% to 8% of the coupling agent; and optionally an additive, a filler, orboth, such that a total percentage by mass equals 100%.
 13. Anelectrical installation box or electrical cable tube, comprising thematerial of claim
 1. 14. A method of imparting flame-retardantproperties to an article, the method comprising adding the material ofclaim 1 to at least one component of the article, wherein the method issuitable for manufacturing electrical installation boxes or electricalcable tubes.
 15. The material of claim 1, wherein the flame-retardantagent consists of a metal hydroxide.
 16. The material of claim 1,wherein the matrix further comprises at least one additional polymerselected from the group consisting of a polycarbonate, anacrylonitrilebutadiene-styrene copolymer, a polystyrene and apolypropylene.
 17. The material of claim 1, comprising from 50% to 65%by mass of the matrix, relative to a total mass of the material.
 18. Thematerial of claim 1, comprising from 35% to 50% by mass of theflame-retardant agent, relative to a total mass of the material.